1. Field of the Invention
This invention relates to a novel linear machine slide. In particular, the invention relates to a design for preloading roller bearings in a linear machine slide to enable frictionless and reproducible operation of the slide.
2. The Prior Art
Preloading of roller bearings in a linear slide is necessary when extremely accurate and lasting performance of the slide is required. Preloading means that the roller bearings are precisely positioned to eliminate side and vertical play, while avoiding friction as well. Such slides are used in machine tools and in inspection and scanning devices in the semiconductor industry, where precise positioning is essential.
Preloading the bearings allows for the slide to be operated at higher speeds and extends its life and cost of operation. The bearings must be mounted to ensure that the preload is evenly distributed over the full length of the raceway. A common method for preload is to apply even amounts of force against an adjustable rail with a set screw in order to obtain a smooth rolling motion and mechanical stiffness.
Various methods are known for preloading roller bearings in slides. For example, U.S. Pat. No. 3,778,121 to Levesque discloses a slide guide having preloaded hollow and solid roller bearings in which the hollow bearings have a diameter slightly larger than the diameter of the bearing surfaces, so that the hollow rollers are compressed between the bearing surfaces. U.S. Pat. No. 3,790,233 to Polidor discloses an antifriction slide assembly in which preload on the rollers is achieved by longitudinal adjustment of a tapered gib having a small wedge angle.
U.S. Pat. No. 5,553,945 to Blaurock et al. discloses a linear guiding apparatus having ball bearings that achieves vibration damping in several ways. One way is to create a slit extending in the moving direction and filling the slit with vibration damping material.
One of the problems with linear machine slides, even when the bearings are precisely preloaded, is that irregularities in the bearing way can detract from the smooth operation of the slide and lead to positioning errors.
It is therefore desirable to construct a linear slide that achieves precise preloading of roller bearings and eliminates movement and vibrations caused by bearing way anomalies, using the spring rate of the carriage housing as a continuously active preload.